The present invention broadly relates to a new and improved construction of rolling or roller mill.
In its more specific aspects the invention relates to a new and improved construction of rolling mill for rolling web-like materials, the rolling mill comprising a roll framework or stand at which there are arranged two work rolls forming a roll gap or nip therebetween acting upon the web-like material in a pressing plane and possibly also having arranged back-up or supporting rolls at the roll stand. At least one of the rolls is designed as a controlled deflection roll including a stationary roll support or beam supported at the roll stand and a rotatable roll shell rotatable about the roll support. The roll shell is supported at the stationary roll by means of support or pressure elements supplied with a pressure fluid or pressurized fluid medium and is displaceable in the pressing plane. An automatic control or regulation device serves to controllably adjust a predetermined thickness of the web-like material subjected to the rolling operation.
Rolling mills as known, for example, from U.S. Pat. No. 4,222,255, granted Sept. 16, 1980, serve to roll metal bands, plastic foils or other plastically deformable materials to a predetermined material thickness. In the most simple case, the rolling mill comprises two work rolls. Additionally, supporting or back-up rolls can be provided in the pressing plane, for example, two supporting or back-up rolls in a so-called four high roll-roller stand, or further supporting or back-up rolls may be arranged in the pressing plane or laterally thereof. It has been found to be very advantageous to design the work rolls or one or a number of the supporting or back-up rolls as controlled deflection rolls in order to exert a defined and adjustable pressure upon the rolled web of material.
A problem in rolling mills of the aforementioned type is the maintenance of a predetermined thickness of the rolled web material. Usually the thickness control, as described, for example, in U.S. Pat. No. 4,074,624, granted Feb. 21, 1978, is performed by sensing the thickness of the web material after the web material has left the roll nip or gap by using a thickness sensor, in order to control and adjust an automatic control or regulator for controlling the pressure of the pressurized fluid medium acting upon the hydrostatic support or pressure elements of the controlled deflection roll such that the material thickness is maintained constant. A disadvantage of this technique is that the thickness sensing or scanning operation has to be accomplished at a certain distance from the roll nip or gap, and thus, with some time-delay. In rapidly running rolling mills the automatic control, therefore, is not rapid enough and there will occur thickness fluctuations, or it will be impossible to increase the rolling speed beyond a predetermined value.
It has been attempted to avoid this disadvantage by controlling the roll nip or gap without any time-delay by using an indirect measurement at measuring points or sites located in the roll framework or stand. Such indirect measurement may be accomplished for example, by measuring the position of positioning or adjustment cylinders for the supporting rolls or the bearing journals thereof as described, for example, in German Pat. No. 2,439,580, granted Jan. 12, 1978, or by performing measurements at the bearing bushings of the roll shell as described in British Pat. No. 2,068,482, published Aug. 12, 1981. It is a disadvantage of these techniques that elastic deformations of the rolls, the bearing journals and the roll stand as well as concentricity or out-of-true running errors in the bearings enter into the measurement and falsify the measuring result. Even the direct measurement of the distance between the supporting rolls, while avoiding the roll stand elongations, still includes the elastic portions of the roll deformation.
While a direct measurement of the distance between the work rolls as described, for example, in British Pat. No. 1,529,861, published Oct. 25, 1978, will render a measurement which is closest to the actual process, such measurement again has the shortcoming that the sensors or feelers are subjected to all sorts of environmental effects like, for example, contamination by metal pieces or spangles, oil used in the rolling process, contaminants or dirt, as well as the action of temperature. Moreover, considering the frequently required change in the work rolls there prevails the danger of damage to the sensors.